The present invention relates to sliding gate valves and components thereof, for use in the pouring of molten metals, and more particularly to their refractory valve plates such as their sliding plates.
The very aggressive conditions to which such valves and their valve plates are exposed when pouring molten metal are recognised to be detrimental to the plates. Despite the use of high-grade, costly refractory materials e.g. high in alumina, valve plates may have to be scrapped after only a few complete pours, or emptyings of a ladle used in supplying metal in a continuous casting plant. Thermal shock is one contributor to damage of valve plates when valves are opened and closed. Another contributor is chemical attack or erosion by metal flowing through the valve. Degradation of valve plates is accelerated when their valves are operated in throttling modes in controlled teeming.
Degradation is usually most marked in sliding valve plates of two-plate valves, and occurs also in the stationary lower plates of three-plate valves. Stationary upper valve plates are not entirely free from degradation either.
Use of refractories better able to resist the adverse service conditions might appear to be one solution. However, even the use of such materials as zirconia might only lead to modest improvements in service life. Routine use of such expensive materials is not cost-effective.
We have recognised that degradation of valve plates is confined largely to areas around or related to their flow orifices and the direction of motion of the sliding plate. From this recognition we have devised a plate construction which may reduce costs involved in scrapping and which facilitates renovation of valve plates.